He will likely be charged with Failure to Surrender to Bail
It is an either-way offence, meaning it can be tried either on summary trial, in the magistrates court (with a maximum punishment of 3 months imprisonment), or on indictment in crown court, which carries a maximum punishment of 12 months imprisonment.
It is likely that in his plea before venue, the magistrates court would deny jurisdiction, and so force the case to be heard in the crown court.
In my opinion, Assange ought to plead guilty at first instance, so he can be awarded the maximum credit for a guilty plea of 1/3 off his sentence. (This credit must be given to Assange)
The court will look at the [Sentencing Guidelines]2. Due to the culpability and extent of his offence, he will probably face the maximum sentence of 12 months.
12 months taking away 4 months for guilty plea, means a sentence of 8 months. A person only serves 1/2 of his sentence (yes, this is a rule), so he will only spend 4 months of that sentence incarcerated, the rest of it will be on license (in America, this will be called on parole).
For more in depth information, along with commentary, A lawyer should consult Blackstone's Criminal Practice.